Pulse width modulated (PWM) signals are frequently used in digital circuitry, such as media processing circuits for use in audio applications, for example, to convert digital signals into an analog output signals. The PWM signals have a duty cycle, which is the ratio of a width of a PWM pulse to a period of the PWM signal, as determined by the PWM frequency. In a particular example, the period or frequency of the PWM signal may be referred to as a PWM frame rate. It is often desirable to convert the duty cycle of the PWM signal into an analog output, which can be used, for example, to control an analog device, such as a motor, a power supply, a speaker, another type of circuit, or any combination thereof.
Unfortunately, to generate a high precision analog control signal, the pulse width of the PWM signals has to be controlled to provide a number of steps that is related to a desired resolution. For example, if a desired resolution is 16-bits, then the pulse width of the PWM signal has to be controllable to provide (216) 65,536 steps within a PWM frame having a frame width (PWM_width) defined by the following equation:
                    step_size        =                              1                          2              16                                *          PWM_width                                    (                  Equation          ⁢                                          ⁢          1                )            In this particular example, if the PWM frame rate or frequency is 100 kHz, the PWM pulse time is 10 μs, which implies a PWM step size of approximately 150 ps. Such a small step size implies a clock speed of 6.5536 GHz, which may be higher than a nominal available clock.
Also, such high clock speeds consume more power than a slower clock. Further, such high clock speeds may not be necessary for other circuitry in a particular circuit device. Hence, there is a need for a digital-to-analog conversion circuit that can provide high resolution at lower clock rates without altering the frequency of the PWM signal.